Implement plan set out in T103206. Make changes to our code and configuration so that we are minimally affected by the following types of failure:

• One payments box becomes unreachable for a few minutes.
• A payments box dies and can be rebuilt with intact data.
• A payments box dies and is rebuilt with no data.

See updated documentation at https://wikitech.wikimedia.org/wiki/Fundraising#Message_queues

Rework code to handle limbo queues as an object rather than a global, and add logic to choose which backends we connect to in each case.

• Frontend code writes to the queue on localhost, aka. payments100[1-3]. No code change, just configuration.
• Orphan slayer connects to these three queues in round-robin order. Configure.
• If the orphan slayer fails to connect to a server, eliminate it from this batch run and hobble on through.
• Configuration for a single queue backend should behave as it did before.